In general, a process for manufacturing a coil spring includes a basic material inspection for a raw material, a surface peeling step, a heating step, a coil forming, and a quenching step.
After a primary coil spring has been manufactured as described above, a series of surface treatment steps are performed to increase mechanical properties and fatigue strength of the coil spring.
That is, after a forming step and a quenching step of the coil spring have been finished, a surface treatment is performed through a tempering step, a shot peening step, a pretreatment step, and a painting step, and a load test step, a marking step, and a final inspection step are then performed before a product is released.
In the heat treatment step and the tempering step, the coil spring is heated to a predetermined temperature, and, at the same time, an internal residual stress of the heat-treated coil spring is removed while the coil spring passes through a heating furnace and a tempering furnace in which a predetermined temperature is maintained, before the coil spring is supplied to a shot peening apparatus.
In the shot peening step, a small ball, such as a bead, made of steel, is shot and collided with the surface of the material, so as to improve mechanical properties of the material and enhance fatigue life of the material. Especially, in the shot peening step, the compressive residual stress distribution of the material can be formed to have a predetermined depth from the material surface, so as to increase the fatigue life and corrosion resistance of the material.
As illustrated in the Korean Registered Patent No. 10-0931155, a conventional shot peening process is performed by interposing a coil spring between spring clamping means facing each other in a state where the coil spring is compressed by the spring clamping means facing each other, and then rotating and shot peening the coil spring by means of a shot room apparatus, wherein the coil spring is moved by a conveyer apparatus.
However, the conventional technique as described above requires a clamping means for holding a coil spring and a conveyer for moving the coil spring, and thus complicates the apparatus and requires a large space for installation thereof.
Also, it is difficult to operate a large number of coil springs in a short time since the coil springs are moved using a conveyer.